log core: Fix issue which could cause piped loggers to be orphaned

and never terminate after a graceful restart. PR 40651. [Joe Orton,
Ruediger Pluem]

log core: fix the new piped logger case where we couldn't connect
the replacement stderr logger's stderr to the NULL stdout stream.
Continue in this case, since the previous alternative of no error
logging at all (/dev/null) is far worse. [William Rowe]

disambiguate an error message to diagnose future error reports

Backport: 452431, 568326, 568322


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@570307 13f79535-47bb-0310-9956-ffa450edef68